Emerging data suggest that maternal vitamin A deficiency may be a risk factor for mother to child transmission of HIV. Among HIV infected women, low serum retinol concentration during pregnancy is a risk factor for infant mortality, mother to child transmission, and higher concentrations of breast milk HIV DNA detected by PCR compared to HIV infected women with normal serum retinol concentrations. These observations suggest that vitamin A supplementation of HIV infected women may reduce vertical HIV transmission rates. Several large trials are currently under way or planned to test this hypothesis. The interaction of vitamin A with HIV, however, appears complex. Some in-vitro data indicates that vitamin A supplementation may benefit the HIV itself. In several studies, pre-treatment of human monocytes or monocyte-like cells with retinoic acid (the intracallular form of vitamin A) prior to infection with HIV increased virus production, and in one study retinol (the form in circulations) and retinyl acetate (the form in food and supplements) produced similar effects leading these authors to conclude that " the use of retinoids in HIV infected patients should be used with caution."